Mobile data transmission and data services are constantly making progress. Typically, mobile communication is based on a mobile communication network infrastructure. Such network infrastructure uses network devices (e.g. network transceiver stations such as evolved Node— B's, eNB's) for enabling communication among terminal devices. Those transceiver stations operate in a specific frequency spectrum specifically assigned to such telecommunication networks. Such assigned frequency spectrum is referred to herein as “licensed” band as it is licensed (reserved) for (exclusive) use by such telecommunication systems. In contrast thereto, “unlicensed” band denotes a band that is not as such assigned for use by the telecommunication infrastructure, but may be used for/by other purposes/communication systems.
With the increasing penetration of such telecommunication services and an increasing number of subscribers and concurrent users of such telecommunication systems, resources (within the licensed band) may often become a bottleneck.
Approaches are therefore being investigated to overcome and alleviate such bottlenecks. One of those approaches is known as device-to-device (D2D) communication, in which devices communicate directly without a network infrastructure being involved.
Currently, device-to-device (D2D) communication is a hot topic which could be used                to improve the resource usage efficiency,        to reduce the power consumption at both network transceiver device (e.g. eNB) and terminal device (e.g. UE) side,        to off load the traffic from the cellular network infrastructure, and also        to possibly enable some new service type in the future.        
At least Qualcomm Inc. has proposed a new study item for the D2D communication in 3GPP TSG-RAN #52 plenary meeting, 31 May-3 Jun. 2011 (cf. RP-110706, “On the need for a 3GPP study on LTE device-to-device discovery and communication”, Qualcomm Incorporated). Although D2D concepts are not yet agreed in current/currently developed mobile communication standards, it is likely to be supported by communication network operators in the near future.
It should be noted that concepts outlined in connection with the present invention are generally independent of any particular communication standard; rather, they are generally applicable to a variety of compatible standards. In order to properly describe the concept(s), however, for explanatory purposes only and without any intention to limit the applicability of the concept(s) introduced in the specification to a particular standard, those concept(s) are described with reference to an example scenario. As the example scenario, LTE (Long Term Evolution) and/or LTE-A (LTE-Advanced) was chosen for the network infrastructure. Likewise, as examples for direct D2D communication scenarios, WLAN (Wireless Local Area Network) also sometimes referred to as WiFI™, Bluetooth™, Zigbee™, or others are known. At least some terminology used herein can also be found in those standards.
Though LTE/LTE-A operates in general on licensed band, it may also be configured to additionally resort to unlicensed band. Currently, unlicensed band(s) available for use, or under investigation to be used, are the ISM band (Industrial Scientific Medical) and White Space (WS) and/or TV White Space (TVWS).
WLAN/WiFi™ Direct is one technique which can realize the D2D function. However, there are many drawbacks inherent to such approach, such as inefficient resource utilization, as well as a somewhat limited coverage.
Hence, it provides the motivation to introduce LTE D2D as a new feature/functionality to LTE/LTE-A. Some features and advantages had been expected from LTE D2D such as interference being controllable by eNB as well as more efficient resource utilization.
For LTE D2D, the operation in both licensed band and unlicensed band needs to be considered. LTE deployment in unlicensed band had been considered as one potential way to reduce the operating cost in future, to improve the system throughput, to off-load (shift) the traffic from licensed band and thus to improve the spectrum efficiency.
Since there are already some local networks deployed in unlicensed band, e.g., WiFi™, Bluetooth™, and Zigbee™, co-existence with other local networks had been considered when deploying LTE in unlicensed band. Considering the low transmit power requirement and short coverage of communication in the unlicensed band, LTE D2D is a more suitable scheme in unlicensed band than deploying the cellular approach from LTE to the unlicensed band(s).
In unlicensed band, however, there is a predefined channelization. That is, the band is divided into individual channels of predefined channel bandwidth. In order to facilitate the co-existence with other local networks, reusing the current channelization is preferred. However, the predefined channel bandwidth may not be fully utilized by communication of one single D2D pair. This may thus still cause inefficient resource utilization in this case.
On the other hand, for LTE D2D operation in licensed band, an eNB can allocate resources for each D2D pair, or allocate resources for a group of devices based on the traffic, so as to enable an efficient resource utilization.
Such centralized resource allocation method, however, can hardly apply directly to a scenario using an unlicensed band due to the fact that the low transmit power in unlicensed band results in a localized interference status. That is, the interference at eNB side will be different from that at device side. This makes it infeasible to let eNB get the channel and allocate it to devices.
Instead, it is more attractive to let devices detect and get the channel themselves. In this case, however, it needs to be considered how to improve the resource efficiency. Namely, considering that there is a predefined channelization in the unlicensed band, and the bandwidth may be too large for a single D2D pair and for some traffic, and the reservation of unlicensed band has to be accomplished in the unit of channel(s), then this will result in inefficient resource utilization in some case.
Thus, there is still a need to further improve such systems in terms of above outlined aspects for D2D communication on unlicensed band.